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Thu, 30 Jul 2020 13:16:44 -0700 (PDT) Received: from xz-x1.redhat.com ([2607:9880:19c8:6f::1f4f]) by smtp.gmail.com with ESMTPSA id t93sm5425890qtd.97.2020.07.30.13.16.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2020 13:16:43 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: peterx@redhat.com, Andrew Morton , Andrea Arcangeli , Mike Kravetz , Matthew Wilcox Subject: [PATCH v2] mm/hugetlb: Fix calculation of adjust_range_if_pmd_sharing_possible Date: Thu, 30 Jul 2020 16:16:36 -0400 Message-Id: <20200730201636.74778-1-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 56AE6100ED0F5 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: This is found by code observation only. Firstly, the worst case scenario should assume the whole range was covere= d by pmd sharing. The old algorithm might not work as expected for ranges like (1g-2m, 1g+2m), where the adjusted range should be (0, 1g+2m) but th= e expected range should be (0, 2g). Since at it, remove the loop since it should not be required. With that,= the new code should be faster too when the invalidating range is huge. CC: Andrea Arcangeli CC: Mike Kravetz CC: Andrew Morton CC: Matthew Wilcox CC: linux-mm@kvack.org CC: linux-kernel@vger.kernel.org Signed-off-by: Peter Xu --- v2: - use min/max instead of custom MIN/MAX [Matthew] --- mm/hugetlb.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 4645f1441d32..7332f3c4b8ec 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5321,25 +5321,21 @@ static bool vma_shareable(struct vm_area_struct *= vma, unsigned long addr) void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end) { - unsigned long check_addr; + unsigned long a_start, a_end; =20 if (!(vma->vm_flags & VM_MAYSHARE)) return; =20 - for (check_addr =3D *start; check_addr < *end; check_addr +=3D PUD_SIZE= ) { - unsigned long a_start =3D check_addr & PUD_MASK; - unsigned long a_end =3D a_start + PUD_SIZE; + /* Extend the range to be PUD aligned for a worst case scenario */ + a_start =3D ALIGN_DOWN(*start, PUD_SIZE); + a_end =3D ALIGN(*end, PUD_SIZE); =20 - /* - * If sharing is possible, adjust start/end if necessary. - */ - if (range_in_vma(vma, a_start, a_end)) { - if (a_start < *start) - *start =3D a_start; - if (a_end > *end) - *end =3D a_end; - } - } + /* + * Intersect the range with the vma range, since pmd sharing won't be + * across vma after all + */ + *start =3D max(vma->vm_start, a_start); + *end =3D min(vma->vm_end, a_end); } =20 /* --=20 2.26.2